In some conventional liquid metering systems, such as, for example, those outputting or discharging hot melt adhesives or other thermoplastic materials, it is usually the practice to output or discharge a predetermined volumetric constant of the particular material. The outputted or discharged materials are pumped through a pump manifold, by means of, for example, suitable metering pumps, to one or more outlets with which suitable output devices or applicators are operatively and fluidically connected so as to deposit the materials onto a suitable substrate in accordance with any one of several predetermined patterns. Such conventional metering systems normally comprise a motor to drive the pumps at variable rates of speed in order to achieve the desired output volumes from the pumps in order to in fact achieve the desired depositions of the materials onto the substrates. Accordingly, the speed of the motor drive, and the result drive of the metering pumps, can be altered depending upon, for ex-ample, the speed of the substrate being processed, that is, for example, the speed of the substrate as the same passes by the output devices or applicators. Depending upon the structure or configuration of the particular substrate or product onto which the hot melt adhesive or other thermoplastic material is being deposited, it is desirable to be able to quickly change the volumetric output of the hot melt adhesive or other thermoplastic material at predetermined times of the material application process, that is, the system must be readily capable of increasing or decreasing the outputted or discharged volumes of the material. While some systems can achieve these changes in the outputted or discharged volumes of material by altering the speed of the pump drive motor, in product process systems, where hot melt adhesive or other thermoplastic materials are being applied to different substrates or products, the product processing speeds, characteristic of hot melt adhesive or other thermoplastic material dispensing metering systems, prevent the change in the speed of the pump motor drive from viably achieving such outputted or discharged volume changes in the hot melt adhesive or other thermoplastic materials as required or desired.
A need therefore exists in the art for a new and improved liquid metering system which is readily capable of rapidly achieving the aforenoted changes in volumetric out-puts of the metering pumps so as to, in turn, achieve the required or desired changes in the outputted or discharged volumes of hot melt adhesive or other thermoplastic material to be deposited onto a substrate or product at predetermined times and/or locations during a product processing run or operation.